Timing of the initiation and duration of the Cretaceous extensional regime in South-east China: Constraints from growth strata in terrigenous basins

Abstract

There has been no consensus yet regarding the precise initial timing and duration of the late Mesozoic extensional tectonics in the South-eastern China Block. This work focusses on the growth strata of the Early Cretaceous red beds in the South-eastern China Block to determine the late Mesozoic tectonics and the precise timing of the initiation and duration of extensional tectonics in this area. Field observation of several terrigenous basins shows that the dip angles of the Cretaceous red beds have varied from moderate to gentle from basin edges to interiors (or centres). The visible and estimated thickness within a single bed increases slightly downwards from the upper to the lower part. These characteristics indicate that the sedimentary area of these beds has undergone an extensional process with expansion and deepening of the sedimentary basins. Rotation of the border surfaces (limbs) and downward warping of the hanging walls or retreat of the footwalls of listric normal faults causes three types of extensional growth (or syntectonic) strata in the deposits of different basins. Dating of the volcanic rocks related to the growth beds reveals that the sedimentary basins were enlarged and deepened when the Early Cretaceous strata were deposited in the South-eastern China Block from ca 140 to 137 Ma. Regionally, under the influence of Palaeo-Pacific plate rollback since ca 140 Ma, the South-eastern China Block stress field has led to lithospheric uplift and pull-apart structures near the surface, causing the half-graben basins to receive sedimentation. Although the extensional event was interrupted by a short compressional event during 120 to 105 Ma, with the oceanward retreat of the trench, the area of extension gradually enlarged and rejuvenated south-eastwards until the end of the Cretaceous. This Cretaceous extension event of the South-eastern China Block must belong to a worldwide geological event with global significance.